1. Field of the Invention
The present invention, in general, relates to woodworking tools and, more particularly, to a guide for use with a router in the cutting of a dado.
Routers are used to cut dados, which are essentially channels, in boards for shelves and other similar purposes. It is important to make the dado cut precisely where desired to prevent damage to the board and also to ensure that all parts align, for example, that both sides of a shelf are parallel. This requires precise location of the dados on each side of the shelf.
Prior types of devices used to cut dados are generally referred to as “dado guides.” However, prior types of dado guides have certain disadvantages. For example, one such type of product that is available from Accurate Woodworking Tools, LLC, 6991 Hollander Lane, Pickett, Wis., 54964, is referred to as their model “ACCURATE GUIDE.”
It relies on a fixture (i.e., the guide portion) that slides along adjacent to a fence. The fence is clamped onto the board to be cut and the fixture is attached to a router by rods that extend away from the fixture. Accordingly, the router is disposed the width of the fixture plus the length of the rods away from the fence.
Two cuts are required for each dado on each board. The first cut is made with the fixture adjacent to the fence. This is difficult because there is no mechanism that ensures the fixture will stay adjacent to the fence. Accordingly, the fixture can pull away from the fence if the user is not careful. One moment of inattentiveness and the board is ruined.
However, there is another substantial disadvantage that occurs when the router is disposed a substantial distance away from the fence. This distance produces a moment arm when pushing on the router with respect to the fence. Accordingly, torque is produced that attempts to twist the fixture relative to the fence (i.e., the router wants to rotate in toward the fence). Absent a mechanism to hold the fixture in position proximate the fence, the fixture can rotate, thereby skewing the cut that is being made and again ruining the board.
If the fixture is adapted to engage with a fence (i.e., to surround a portion of the fence on both sides), then the torque that is produced tends to bind the fixture relative to the fence, making it especially difficult to urge the router along the longitudinal length of the fence.
Another disadvantage with prior art fixtures (dado guides) is that the attachment of the router to the fixture produces a relative, changing, and unpredictable distance between the two. It depends on how deep the rods are attached to the fixture and how deep the rods are inserted into the base of the router itself. There is no fixed distance from the router bit to the fixture. Accordingly, there is no way to determine where the cut will actually occur by use of the fixture. Careful measurement is required which is, at best, a guess that is anything but precise.
A further disadvantage is that after the first cut is made, a piece of scrap wood from the shelf or board that will be placed into the dado must be inserted into the fixture itself. This introduces an offset sufficient to displace the router further away from the fence an amount equal to the thickness of the board that will be inserted into the dado.
There are numerous disadvantages with this approach. The most obvious disadvantage is that there simply may not be a scrap piece of wood available if the entire length of the board placed in the dado is to be used. For example, a person can purchase several three-foot long shelves, already cut, and plan on using them to make a bookcase. There are no scrap pieces available in this instance.
First, the cutting operation must be interrupted (i.e., stopped) in the middle of each dado that is being formed and the fixture adjusted prior to finishing the dado. This is time consuming.
Second, the scrap wood must be inserted into a particular slot depending upon the size of the router bit and the thickness of the dado cut. If the scrap wood is inserted in the wrong slot, a dado that is too large can be produced, thus ruining the entire board (which likely is the side of a bookcase, etc.).
Third, after this adjustment is made, the router is displaced away from the cut that has already been made. If the dado extends from end to end, then there is no problem associated with this displacement. The next cut is made from beyond one end of the board extending past the other end.
However, if the dado is contained within the board (i.e., if it does not extend to the ends of the board), then, after having displaced the router further away from the fence, the new cutting position of the bit will interfere with the wood. This might result in possibly requiring a further changing of bits (i.e., to a new bit that can cut on its bottom) in order to penetrate the wood and allow finishing of the dado, after again changing back to the original bit (that cuts on its circumference, but not on its bottom). This greatly extends time to complete each dado.
There is another problem associated with the use of routers making two passes to cut a dado. The first pass is typically made in a first direction, and the second pass is typically made in an opposite second direction. In one direction, the router bit itself is rotating and tends to pull the router toward the fence. In the opposite direction, the router bit tends to urge the router away from the fence. Motion in either direction can ruin the board that is being cut. This is difficult, especially for unskilled users, in that sufficient skill and anticipation of the router-introduced forces are not yet developed.
Accordingly, there exists today a need for a dado guide that helps ameliorate these disadvantages. Clearly, such an apparatus would be a useful and desirable device.
2. Description of Prior Art
Dado guides are, in general, known and are similar to the above-described device available from Accurate Woodworking Tools, LLC. In general, the router is displaced away from a fence and produces substantial torque when pushed. The cutting procedure for each dado must be interrupted (i.e., it cannot be a continuous operation). Scrap boards are required to adjust the cutting width. A lack of precision in setup, as well as location of the actual dado, is inherent with all known prior art devices.
While the structural arrangements of the above-described devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.